A brake system of a vehicle is a system for maintaining a parking state while decelerating or stopping a driving vehicle.
The brake system generally converts kinetic energy into thermal energy by using friction force to discharge the thermal energy into the atmosphere and generate brake force. While a brake disk that rotates together with a wheel is pressed by brake pads at both sides of the brake disk by using hydraulic pressure, the vehicle is braked.
However, as the existing hydraulic brake system is implemented in such a manner to strongly push the brake pad toward the brake disk by using the hydraulic pressure while braking, the existing hydraulic brake system cannot but have a complicated configuration by a master cylinder which is actuated through a booster that boosts pedal operation force to generate the hydraulic pressure and a hydraulic line connected to a wheel cylinder, and various devices that control and assist the master cylinder and the hydraulic line and there is weakness that improvement of reliability and stability is limited due to the configuration complexity and braking performance depending on the use of the hydraulic pressure.
As a result, simplicity of the configuration which the hydraulic brake system cannot have is implemented in the vehicle and an electro-mechanical brake (EMB) which can strengthen the reliability of the braking performance is used.
In the electro-mechanical brake (EMB), when a brake pedal is pressed for the purpose of braking the vehicle, a 3-phase winding permanent magnet type synchronous electric motor, for example, a BLDC motor which is a 3-phase motor is actuated, and as a result, a pistol installed in the master cylinder moves to generate hydraulic pressure required for braking, thereby actuating a brake.
Meanwhile, in order to control the 3-phase motor, the location of a rotor included in the motor becomes an important control factor and a hall sensor and an encoder are used for detecting the location of the rotor.
However, in an electronic brake system using the 3-phase motor, there is a problem in that an initial angle of the encoder cannot be known when the motor initially starts. As a result, the electronic brake system operates by acquiring the initial angle by using the provided hall sensor and when the hall sensor is not provided or when the hall sensor is abnormal, the initial angle cannot be known, there is a problem in that starting the motor is impossible.
Therefore, while controlling the 3-phase motor in the electronic brake system, the hall sensor is fixed or even when there is no hall sensor, a research into sensing the location of the rotor of the motor by using the encoder is in progress.